Spontaneous emission enhanced heat transport method and structures for cooling, sensing, and power generation

ABSTRACT

A method and structure for heat transport, cooling, sensing and power generation is described. A photonic bandgap structure ( 3 ) is employed to enhance emissive heat transport from heat sources such as integrated circuits ( 2 ) to heat spreaders ( 4 ). The photonic bandgap structure ( 3 ) is also employed to convert heat to electric power by enhanced emission absorption and to cool and sense radiation, such as infra-red radiation. These concepts may be applied to both heat loss and heat absorption, and may be applied to heat transport and absorption enhancement in a single device.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and a structure forheat transport, and more particulary to a method and a structure forspontaneous emission enhanced heat transport for cooling, sensing andpower generation. The present invention also relates to methods andstructures for cooling, sensing and power generation.

[0003] 2. Discussion of the Background

[0004] For a long time the spontaneous emission of light was considereda natural and immutable property of radiating atoms. However, Purcellshowed that an atom in cavity would radiate faster than an atom in freespace (E. M. Purcell, Physical Review, 69, 681 (1946)). Purcellindicated that the spontaneous emission at wavelength λ will beincreased by a factor f given by, f˜(λ³/a³), where a is the dimension ofthe cavity. For example, Purcell suggested that incorporating metalparticles of 10⁻³ cm diameter in a matrix can cause the spontaneousemission rate at radio frequencies, 10⁷ Hz (λ˜3×10³ cm), to increase bya whopping f˜λ³/a³=(3×10³)³/(10⁻³)³˜2.7×10¹⁹ times. Thus the thermalequilibration time constant at radio frequencies will come down from5×10²¹ sec to only 3 minutes.

[0005] From Planck's radiation law, the spontaneous emission atfrequency ν is derived from a probability A_(ν), given by

A _(ν)˜[8πhν ³ /c ³]  (1)

[0006] The above coefficient A_(ν) gets modified by the Purcell factor,f, indicated above,

[0007] Now, consider spontaneous emission at or near room temperature.Wein's Law gives the peak emission wavelength (λ_(T)) at a temperatureT:$\frac{\lambda_{T} - {2.89 \times 10^{- 3}\quad {Km}}}{T\quad \left( {{in}\quad K} \right)}$

[0008] For the purpose of this discussion, consider the radiativeemission at this peak wavelength. The following equation is obtained:

λ_(300k)˜9.67 μm or ν_(300k)˜3.1×10¹³ Hz.

[0009] Compared to spontaneous emission at radio frequencies (ν˜10⁷ Hzdiscussed above), the probability of the spontaneous emission (at 300K)at far-infrared wavelengths (ν˜3.1×10¹³ Hz) is already high from eqn.(1). It is for this reason, all bodies are observed to radiatesignificant amount of radiation at 300K. This is the basis for imagingusing IR wavelengths.

[0010] Even though the above spontaneous emission at IR wavelengths issignificantly useful for IR imaging purposes, the energy loss(dissipative transfer) from spontaneous emission of a body even at aslightly higher temperature than 300K is rather small. The energy flux(Φ) radiating from a blackbody at temperature (T) including allfrequencies is given by the Stefan Boltzmann Law:

Φ=εσT ⁴

[0011] where

[0012] ε=emissivity, and

[0013] σ=Stefan Boltzmann constant=5.672×10⁻⁵ erg/sec 1/cm² deg⁴

[0014] =5.672×10⁻¹² W/cm² 1/deg⁴

[0015] For a blackbody with ε=1 at T=300K, the following is obtained:

Φ≅4.39×10⁻² W/cm ²  (2)

[0016] From a heat-spreader point of view, as used in many electronicsand other sensitive cooling applications around 300K, this Φ is small.Hence most of the heat that is removed from the electronics (like amodern day 1.2 GHz Pentium® processor) is achieved through a convectiveprocess (blowing air across fins) or through otherconductive/heat-transfer process (flowing liquid) as in manytop-of-the-line servers and main-frame computer electronics. These heattransfer processes are at best modest just enough that the Pentium® chipdoes not overheat or that the reliability of the servers are not indoubt. However such solutions are insufficient for many future coolingapplications in computer electronics operating in the 2 GHz range andabove. This will be especially true if high-performance thin-filmthermoelectrics are used to actively pump the heat from the chip, whenthe power density levels that need to be dissipated (taking into accountsome heat-spreading effects from the source to the spreader-sink side)can easily be in the range of several to tens of watts/cm². See L. H.Dubois, Proc. of 18^(th) International Conference on Thermoelectrics, 1,(1999), IEEE Press. Catalog No. 99 TH8407 and references cited in thisarticle.

[0017] For spot-cooling of high-power electronics and high-power VCSELS,simple convective cooling processes are insufficient. Also, the abovemethods of cooling with blowing air or flowing liquid are cumbersome andintroduce unwanted complexities to systems.

SUMMARY OF THE INVENTION

[0018] It is an object of the invention to provide a method for and astructure having enhanced heat transfer.

[0019] It is also an object of the invention to provide a method for anda structure having enhanced heat transfer through spontaneous emission.

[0020] It is a further object of the invention to provide a method forand a structure having the ability to absorb the IR radiationefficiently thus leading to a better sensing device.

[0021] Still another object of the invention is to provide a method forand a structure having the ability to absorb the IR radiationefficiently thus leading to a better thermal-to-electrical powerconversion device.

[0022] Yet another object of the invention is to provide hand-heldcomputational and communication devices with power using athermal-to-electrical power conversion device according to theinvention.

[0023] These and other objects may be obtained using a heat transferstructure having a heat spreader, a photonic bandgap structure connectedto the heat spreader, and a defect cavity formed in the photonic bandgapstructure. A region in the heat spreader may be arranged to receive heatfrom a heat source, and the defect cavity may be positioned adjacent tothe region. A thermoelectric device may also be connected to the heatspreader.

[0024] The photonic bandgap structure may comprise an array of columnarstructures formed around the cavity. The columnar structures may have adiameter and a spacing based upon a wavelength of emitted radiation.

[0025] The photonic bandgap structure may also comprise a high thermalconductivity material with one of metal, semi-metal and semiconductorparticles disposed in the material. The particles may have an infraredtransmission property different from infrared transmission properties ofthe material. The particles may be separated in the material by one halfto three times a wavelength of an infrared emission peak correspondingto the respective temperature of the structure.

[0026] The photonic bandgap structure may also comprise microfinsenhancing both radiative and emissive heat transport.

[0027] The objects of the invention may also be obtained by a method ofheat transport comprising removing heat from a heat source and using aphotonic bandgap structure to allow radiative heat transport andenhancing emissive heat transport. The method may also include steps ofdisposing a defect cavity in the photonic bandgap structure, positioningthe cavity to be aligned with heat transport from the heat source,disposing a plurality of defect cavities in the photonic bandgapstructure, and positioning a plurality of cavities to be respectivelyaligned with heat transport from plurality of heat sources.

[0028] The device according to the invention can have the photonicbandgap structure connected to the heat spreader. The photonic bandgapstructure may also be formed as part of a heat spreader. In the case ofthe heat source being an electronic integrated circuit, the photonicbandgap structure may also be formed as a part of the substrate of theintegrated circuit or device.

[0029] The device according to the invention may also be a sensingdevice having an infrared sensor with a sensing surface and a photonicbandgap structure disposed to enhance coupling of infrared radiation tothe sensing surface.

[0030] The device according to the invention may also be athermal-electric conversion device comprising a heat absorption element,a heat-to-electric conversion device coupled to the element and aphotonic bandgap structure disposed to enhance coupling of heat to saidheat absorption device. In a further embodiment, the device according tothe invention may comprise a sensing device having an infrared sensorand a first photonic bandgap structure, and an infrared enhancingemission structure disposed to enhance emission of infrared radiation tothe sensor and comprising a second photonic bandgap structure.

[0031] In yet another embodiment, a device may comprise athermal-electric conversion device having a heat absorption element, aheat-to-electric conversion device and a first photonic bandgapstructure, and a heat absorption device and a heat enhancing emissionstructure disposed to enhance emission of heat to the element andcomprising a second photonic bandgap structure.

[0032] The devices according to the invention may be sized to behand-held, and the devices according to the invention may be adapted tosupply converted power to a hand-held electronic device. The devicesaccording may also be adapted to absorb beat from a waste heat source,such as the hand of a person.

[0033] Since good emitters are good absorbers, the concepts presentedfor increased spontaneous emission are equally applicable to structuresdesigned increased absorption. Thus, these concepts are applicable tosensing of infrared radiation useful in infrared sensors as well asgeneration of electrical power based on absorbing heat radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1A is a diagram of a first embodiment of the device accordingto the invention;

[0035]FIG. 1B is a diagram of a modification of the first embodiment ofthe device according to the invention;

[0036]FIG. 1C is a diagram of another modification of the firstembodiment of the device according to the invention;

[0037]FIG. 1D is a diagram of another modification of the firstembodiment of the device according to the invention;

[0038]FIG. 1E is a diagram of the device of FIG. 1A illustrating regularheat dissipation and radiative heat emission;

[0039]FIG. 1F is a diagram of the device of FIG. 1D illustrating regularheat dissipation and radiative heat emission;

[0040]FIG. 2A is a diagram of a photonic bandgap structure having asquare cavity;

[0041]FIG. 2B is a diagram of a photonic bandgap structure having ahexagonal cavity;

[0042]FIG. 2C is a diagram of a photonic bandgap structure having acircular cavity;

[0043]FIG. 2D is a perspective view of the diagram of a photonic bandgapstructure having a cavity;

[0044]FIG. 3 is a diagram illustrating the size and spacing of thearrayed structures in a photonic bandgap structure;

[0045]FIG. 4 is a diagram of a second embodiment of the device accordingto the invention;

[0046]FIGS. 5A and 5B are side and bottom diagrams, respectively, of astructure according to the invention;

[0047]FIG. 6 is a diagram of a multi-chip module according to theinvention;

[0048]FIG. 7 is a diagram of a three-dimensional multi-chip moduleaccording to the invention; and

[0049]FIG. 8 is a diagram of a hand-held device using a heat transportdevice according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] According to the invention, enhanced radiative heat transfer ofheat from a semiconductor chip, or other device or structure requiringcooling, is obtained. This may be accomplished by integrating a photonicbandgap structure with a heat spreader or on the device or structurerequiring cooling. Spontaneous emission (at far-infrared wavelengths) isenhanced for increased radiative heat loss.

[0051] A schematic diagram of a photonic bandgap structure according toa first embodiment integrated onto a heat spreader is shown in FIG. 1A.Here, an active thermoelectric (TE) device 3 pumps heat from the desiredregion, such as active region 1, of a semiconductor device 2. Device 3may be a thin-film TE device that can pump heat at >100 W/cm² at pointA. The heat that is pumped by the TE device 3 is dumped at heat spreader4 at point B. Heat spreader 4 can be made of a number of materialshaving high thermal conductivity, such as diamond or SiC.

[0052] Heat spreader 4 is shown to have about the same dimensions of thedevice 2, and TE device 4 is shown to have similar dimensions to activeregion 1. This is merely for illustrative purposes and the invention isnot so limited. For example, the active region may cover most of thesurface of device 2, and the spreader may be of smaller or largerdimensions compared to device 2, depending upon the application, desiredresults or other factors.

[0053] The heat spreads from B to C, the location of the ultimateheat-sink. Going from points B to C, depending on the thermalconductivity and thickness of the spreader, the power density at C canbe in the range of 5 to 10W/cm² for a thin-film TE device pumping at 100W/cm². For a bulk TE device, with a cooling power density of only 5 to10 W/cm², the power density at C would be in the 0.5 to 1 W/cm². Notethat from eqn. (2)

Φ≅4.39×10⁻² W/cm ²<<5 to 10 W/cm ²

[0054] obtained with the conventional heat spreaders, i.e., without thephotonic bandgap/defect structure combination according to theinvention.

[0055] Attached to or incorporated into spreader 4 is a photonic bandgapstructure (PBS) 5. PBS 5 is preferably made of the same material as theheat spreader 4, but it not necessary. A PBS made of a differentmaterial could also be attached to the heat spreader in intimate thermalcontact. A defect cavity 6 may be formed at the center of PBS 5. If sucha PBS material is integrated with a defect cavity 6, as shown in FIGS.2A and 2B, then cavity 6 will show enhanced radiative heat loss at λ≅10μm. There will also be improvement at other wavelengths, for exampleλ≦10 μm. Note that the enhanced radiative property comes from theinteraction between the PBS and the adjoining cavity, where the heat isto be dissipated. Thus defect cavity 6 of PBS 5 preferably coincideswith the heat-spreading area directly below the active-heat generatingarea A as shown in FIG. 1. Such a structure is termed a SpontaneousEmission Enhanced Heat Transport (SEEHT), achieved here using photonicbandgap structures.

[0056]FIG. 1B illustrates a modification of the embodiment of FIG. 1Awhere the TE device 3 is omitted and the heat spreader 4 with PBS 5 isattached directly to the device 2, at the backside. A furthermodification is shown in FIG. 1C where the separate heat spreader isomitted and the PBS 5 is attached directly to the device 2, at thebackside. PBS 5 can be located at a position other than the backside.For example, PBS 5 and the associated defect cavity can be located abovethe active region. Lastly, FIG. 1D shows a modification where the PBS 5is formed as part of the device 2.

[0057] More detailed views are shown in FIGS. 1E and 1F. In FIG. 1E,shown with the device of FIG. 1A is the enhanced heat dissipation 8,i.e. convective heat loss, and enhanced radiative heat emission 9. Thedissipation 8 may also contain a component from the structures in PBS 5acting as microfins (not shown). In FIG. 1E, the heat transferefficiency by the radiative process is enhanced also due to the leakageof modes from the cavity area (where heat arrives from the chip byspreading) to the PBS area similar to enhanced photoluminescenceefficiency in light emitting diodes. FIG. 1F shows the heat dissipation8 and heat emission 9 in the structure of FIG. 1D.

[0058] An example of PBS 5 according to the invention is shown in FIGS.2A-2C. PBS 5 contains cavity 6 and photonic bandgap structures 7consisting of columnar structures spaced in an array. Cavity 6 is squarein FIG. 2A, hexagonal in FIG. 2B, and circular in FIG. 2C, but it isnoted that other shapes are possible. The cavity interrupts theperiodicity of the photonic bandgap structures 7. This dramaticallyincreases the spontaneous emission and thus dramatically increases theheat dissipation.

[0059] Also, the size of cavity 6 may be varied, depending upon theapplication. The cavity usually should be larger than the individual PBScolumnar structures to create interruption in the photonic bandgapstructure. Close packing is a consideration. Also, the size can beoptimized based upon the peak-producing area and the enhancement factorfrom the Purcell effect. The size may also be chosen in relation to thesize of source of heat or the size of the heat transfer path.

[0060] The defect cavity 6 surrounded by the photonic bandgap structureshown in FIGS. 2A and 2B can provide at least a ten-fold enhancement inspontaneous emission intensity (i.e., radiative heat loss capability)where it is needed. Higher enhancement factors can be obtained withsmaller cavity sizes, i.e., small areas where heat is generated. Inother words, the cavities can be strategically placed to remove heatfrom one or many specific areas.

[0061]FIG. 2D is a perspective cross-sectional view of PBS 5 of FIG. 2A.Structures 6 and 7 may be formed by etching the material of PBS 5 usingknown etching techniques, such as those employed in semiconductorprocessing. For example, dry or wet etching using a masking material maybe used to define structures 7. Structures 7 may be separately formedand integrated with a heat spreader.

[0062] In a more specific example illustrated in FIG. 3, for λ≅10 μm,corresponding to the peak wavelength at 300K, a, the lattice spacing forthe photonic bandgap is

a/λ=0.5 or a≅5 μm

[0063] and the radius r for a circular structure is

r/a≅0.45 or r≅2.25 μm

[0064] Thus in FIG. 3, with a=5 μm and r≅2.25 μm, a photonic bandgapstructure with a pitch around 10 μm results. Note that although thisdesign is for 10 μm and the radiative emission occurs over a broad rangeof wavelength around 10 μm, proportional improvement may be expected atother wavelengths as well.

[0065] Note that this design is for λ≅10 μm, corresponding to the peakwavelength at 300K. If heat sink or device operates at highertemperatures, such as 400K, then the expected peak λ˜7.3 μm. For aboveexample, a, the lattice spacing becomes ˜3.7 μm, and r, the diameter ofthe structure would be ˜1.7 μm. Such operating temperatures are likelyto useful for high-temperature Si power electronics heat spreadingapplications and high-temperature/high-power SiC and GaN deviceapplications.

[0066] If the PBS is to be designed for lower heat sink temperaturessuch as 77K, then the expected peak λ˜38 μm. In the above example, awould be ˜19 μm, and r would be ˜8.6 μm. Obviously, such larger “a” and“r” should be easier and cheaper to achieve in practice. Such heatspreaders are likely to be useful for low-temperature applications as inlow-temperature electronics, superconducting motors and generators.

[0067] Heat spreader 4 has dimensions h₁ and h₂ shown in FIGS. 1A and1E. Typically, in a heat spreader, it is preferable to minimize h₁ toeffectively dissipate the arriving heat at B. However, the physicalhandling of the heat spreader poses certain limitations on minimalthickness. In the heat spreader shown in FIGS. 1A and 1E, h₁ ispreferably in the range of 25 μm to 300 μm. The dimension h₂ is likelyto dominated by the consideration of the thickness of the desiredstructures that can be produced reliably. The ratio of thickness of h₂relative to h₁ can be maximized, if necessary. The dimension h₂ could bein the range of about 1-10 μm for application at 300K.

[0068] In FIG. 1D, a further modification of the FIG. 1A structure isshown, where the bottom-side of the substrate (which contains theelectronics) itself is patterned to achieve similar spontaneous-emissionenhanced heat removal. Of course, this avoids the use of the heatspreader as well as the thermoelectric device. Such an arrangement isconceivable in Si-based electronics as Si, with its high thermalconductivity, can serve as the heat spreader as well as thespontaneous-emission enhanced emitter. Also, note the distinctionbetween the heat waves and the light waves. Note again the distinctionbetween the regular heat dissipation and the additional spontaneousemission enhanced light waves is indicated in FIG. 1D.

[0069] It is also conceivable that the spontaneous emission light wavescould be absorbed by a black body absorber (not shown) that ismaintained at a lower temperature by a mechanism such as thermoelectriccooling or liquid cooling.

[0070] A second embodiment of an enhanced spontaneous emission deviceaccording to the invention is shown in FIG. 4. Conductive particles 11are incorporated into the heat spreader to produce an enhanced radiativeheat emitter 10. As an example, approximately 2 μm particles (metal) areincorporated in a heat spreader like SiC, AlN or Si. The Purcellenhancement factor f, at ≅300K, for spontaneous radiative emission wouldbe, for λ≅10 μm and a≅2 μm:

f≅λ ³ /a ³≅125

[0071] Thus from eqn. (2) and the f of 125, we obtain for the structureof FIG. 4:

Φ≅125×4.39×10⁻² W/cm ²≅5.5W/cm ²

[0072] If 1.0 micron size particles are incorporated, then the radiativeemission enhancement can be as much as a factor of 1000, over aconventional heat spreader, leading to a Φ of 44W/cm². If such micronsize particles can be incorporated by impregnation orself-assembly-followed by overgrowth, then the scope for radiative heatloss mechanisms would be considerably enhanced.

[0073] The particles 11 can be made of metal, semiconductor, semimetalin a matrix of a high-thermal conductivity heat spreader such as SiC,AIN, Si, diamond, etc. The particles 11 are preferably chosen so thattheir infrared emission characteristics are different from that of theheat spreader so that the substrate matrix and the particle do not forma continuum from an electromagnetic emission standpoint. These emissioncharacteristics in turn can be traced to their complex refractiveindices at the wavelength of interest. It is expected that even a fewpercent difference in the refractive index between the particle and thesubstrate matrix may produce sufficient enhancement in spontaneousemission rates. A larger difference in the refractive index will alsobenefit the enhancement.

[0074] It is also preferable that the particles are separated from eachother (in linear distance) by about one half to three times thewavelength of the IR emission peak corresponding to the respectivetemperature. For example at a temperature of 300K, with the emissionpeak at 10 microns, the spatial separation between adjacent 1 micronparticle could be anywhere between 5 microns to 30 microns. Theefficiency of the radiative emission process could depend on thisspatial separation due to the coupling between the these particlesforming a continuum. Regular heat dissipation 8 and the additionalspontaneous emission enhanced light waves 9 are also indicated in FIG.4. Note that such an ordered assemblage of micron size particles withseveral micron size separation may be fabricated with epitaxial orchemical vapor deposition or simple chemical processes (like colloidalchemistry) self-assembly methods. In addition, in FIG. 4, thin-filmthermoelectric cooling devices 3 may be incorporated (similar to FIG. 1)to combine high-cooling power density active-cooling with high-fluxdensity radiative heat dissipative processes.

[0075] Such spontaneous high radiative heat fluxes near 300K would makethe heat-removal problem much more manageable in future electronicscooling. This could obviate the need for liquid heat transfer processes.Thus it should be possible to make an all solid-state,spontaneous-emission-enhanced-refrigeration (SEER) systems with orwithout thermoelectric cooling devices. The thermoelectric devices wouldbe used where active cooling is needed. Certainly, these SEEHT devicesmay be necessary for thin-film devices. However, even bulkthermoelectric devices with a heat flux of about 0.5 W/cm² at theheat-sink stge could benefit from these concepts.

[0076] Another possible modification to the structure of FIG. 1A forenhancement of spontaneous emission as applied to enhanced heat removalcould be to pattern micron-sized (1 to 20 μm) structures 12 on the heatspreader 4, as shown in FIGS. 5A and 5B. No defect cavity is included.The structures double for micro-fins and thus also enhance spontaneousconvective heat loss. For example, an approximately 2 μm structure couldbe patterned on the heat spreader 4 using standard photolithographictechniques. These 2 μm geometries should be easily achievable withtoday's lithography in large-area geometries for a cost-effectiveimplementation. Note again the distinction between the regular heatdissipation and the additional spontaneous emission enhanced light wavesis indicated in FIG. 5A. Size and pattern differneces for thesestructures are anticipated based on an f≅λ³/a³—like enhancement factor.

[0077] As noted earlier, with the use of spontaneous emission enhancedheat transport structures (SEEHT) it is possible to implement effectivecooling strategies (with or without thermoelectrics) in an allsolid-state system. Such an advantage is illustrated for a multi-chipmodule in FIG. 6. Note that this schematic (showing integration in avertical direction) can be scaled in the lateral dimension as well toproduce a 3-dimensional multi-chip module (MCM). Such a 3-D MCM couldhave thermoelectric devices for cooling at various chip levels and theheat could be radiated from the periphery (both outer-ring, andinner-ring) using SEEHT structures.

[0078] Module power lines 20 and module signal line 21 are shown onspreader 22. Formed on both sides of spreader 22 are PBS structures 23.In this example the structures are the conductive materialimpregnated-type PBS structure, but it is understood that the other PBSdescribed above may also be used. Thermoelectric cooling devices 24remove heat 27 from electronics chip or device 25. Power is supplied tothe TE devices 24 at 26. Inter-level signal paths 28 and inter-levelpower paths 29 are also shown, as well as inter-level TE powerconnection 30 and uni-level or intra-level connection 31. Any number ofarrangements are possible.

[0079] A schematic diagram of such a 3-dimensional spontaneous emissionenhanced heat transport multi-chip modules (3-D SEEHT-MCM) is shown inFIG. 7. Liquid-cooled heat-absorbing blackbody cores 40 and 41 can beincorporated inside the ring and outside the ring for absorbing theradiant heat emanating from the SEEHT structures 43 in the periphery.SEEHT structures 43 have heat spreaders with thermoelectric devices 44.Shown at 45 are SEEHT structures with conductive-particle impregnatedPBS structures. Although the SEEHT devices are shown alternating as 44and 45, other arrangements are possible. The cores are kept cooled toincrease the temperature differential between them and the SEEHTstructures, thereby enhancing radiative heat absorption. The cores couldbe appropriately coated with high-emissivity (therefore absorptivity)materials to facilitate this process. Note that the “liquid” cooling isconfined to areas where active electronics is absent. Thus, the systemcomplexity in these situations ran be considerably reduced.

[0080] The present invention offers a new approach to efficient heatspreaders termed SEEHT using enhancement of spontaneous radiant emissionof heat at long IR-wavelengths. Under certain situations these SEEHTstructures could also benefit from periodic PBS, invoking Braggscattering thereby preventing emission trapping, specifically tailoredfor the long IR-wavelengths. The periodic structures around the defectcavity in FIGS. 1A-1D and 2A-2C serve this purpose and could beimplemented suitably in the SEEHT exiting surfaces of FIG. 1. Note thatthe dimensions of such PBS for the long-wavelengths are in the range of2 μm, considerably larger (and so easily implementable with low-costlithography) than the sub-micron features needed for the application ofPBS to LED's at the visible and near-IR wavelengths.

[0081] Two other modifications are also possible in light of the aboveteachings. One involves the use of similar concepts to obtain what canbe described as spontaneous-absorption enhanced sensors (SAES). Thisstems from the general idea that good absorbers are good dissipaters.The above described concepts to enhance energy flux radiating from ablackbody at temperature (T) are also applicable to energy flux that canbe radiatively absorbed by a blackbody at a temperature (T). This canhelp in designing improved infra-red sensors to detect temperatures ofobjects. In this case the PBS structures described above are applied tothe surface of the blackbody or sensor to enhance the absorbedradiation. Defect cavities may be used, but are not necessary ifstructures like FIG. 4 are used for enhanced absorption.

[0082] Another involves the use of similar concepts to obtain what canbe described as spontaneous-absoption enhanced thermal-to-electricalconverters (SAETEC). The above described concepts to enhance energy fluxradiating from a blackbody at temperature (T) are also applicable toenergy flux that can be radiatively absorbed by a blackbody at atemperature (T). This can help in designing improvedthermal-to-electrical power sources. For example, in hand-held devicesas shown in the FIG. 8, a SAETEC device can better absorb the heatradiated by the hand which in turn can be converted into electricity bydevices such as thermoelectric power converters. The heat from a hand isin the range of 10-15 W. Also, a spontaneous emission enhanced heattransport (SEEHT) device can be worn on the hand thus efficientlyradiating the heat from the palm of the hand. Thus a combination of theSEEHT device and SETEC device can be used to maximize the power fed tothe hand-held device, augmenting its battery back-up or replacing itsbattery or reducing the need for its recharging of its batteries moreoften.

[0083] The SETEC can also double as a detector, or incorporate adetector, so that when a user picks up the hand-held device, the heatfrom the hand is detected and actives the hand-held device.

[0084] Numerous other modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent invention may be practiced otherwise than as specificallydescribed herein. For example, the PBS and SEEHT structures may beattached to or formed in devices or structures other than thesemiconductor-type devices described above. The principles of theinvention are applicable to a wide range of cooling applications,devices needing cooling such as biological devices, mechanical devices(producing heat within themselves), power generation devices (producingheat in various parts), piezoelectric devices, magnetic devices, opticaldevices, ceramic devices and plastic devices.

What is claimed as new and desired to be secured by Letters Patents ofthe United States is:
 1. A heat transfer structure, comprising: a heatspreader; a photonic bandgap structure connected to said heat spreader;and a defect cavity formed in said photonic bandgap structure.
 2. Astructure as recited in claim 1, comprising: a region in said heatspreader arranged to receive heat from a heat source; and said defectcavity positioned adjacent to said region.
 3. A structure as recited inclaim 1, comprising: a thermoelectric device connected to said heatspreader.
 4. A structure as recited in claim 1, wherein said photonicbandgap structure comprises: an array of columnar structures formedaround said cavity.
 5. A structure as recited in claim 4, comprising:said columnar structures having a diameter in the range of about 1.7-8.6microns
 6. A structure as recited in claim 5, comprising: said columnarstructures having a diameter of about 2.25 microns and spacing of about5 microns.
 7. A structure as recited in claim 1, wherein said photonicbandgap structure comprises: a material having a plurality of conductiveparticles disposed therein.
 8. A structure as recited in claim 7,wherein: said material comprises a high thermal conductivity material;and said particles comprise one of metal, semimetal and semiconductorparticles disposed in said material.
 9. A structure as recited in claim7, comprising: said particles having infrared transmission propertiesdifferent than infrared transmission properties of said material.
 10. Astructure as recited in claim 7, comprising: said particles beingseparated from each other by about one half to three times a wavelengthof an infrared emission peak corresponding to the respective temperatureof said structure.
 11. A structure as recited in claim 7, comprising:said particles having a size of about 1 micron and separated from eachother by a distance between about 5 and 30 microns.
 12. A structure asrecited in claim 1, wherein said photonic bandgap structure comprises:microfins enhancing both radiative and emissive heat transport.
 13. Amethod of heat transport, comprising: removing heat from a heat source;and using a photonic bandgap structure to allow radiative heat transportand enhancing emissive heat transport.
 14. A method as recited in claim13, comprising: disposing a defect cavity in said photonic bandgapstructure.
 15. A method as recited in claim 14, comprising: positioningsaid cavity to be aligned with heat transport from said heat source. 16.A method as recited in claim 14, comprising: disposing a plurality ofdefect cavities in said photonic bandgap structure.
 17. A method asrecited in claim 14, wherein said heat source comprises a plurality ofheat sources, comprising: positioning said plurality of cavities to berespectively aligned with heat transport from said plurality of heatsources.
 18. A semiconductor device, comprising: a substrate; an activearea disposed in said substrate and generating heat; a heat spreaderdisposed on said substrate; and a photonic bandgap structure connectedto said heat spreader.
 19. A device as recited in claim 18, comprising:a thermoelectric device disposed between said substrate and said heatspreader.
 20. A device as recited in claim 18, comprising: a defectcavity formed in said photonic bandgap structure; and said cavityarranged to be aligned with said active area.
 21. A device as recited inclaim 18, comprising: a plurality of active areas disposed in saidsubstrate; a plurality of defect cavities formed in said photonicbandgap structure respectively arranged to be aligned with saidplurality of active areas.
 22. A device as recited in claim 18, wherein:said heat spreader comprises a first portion of said substrate; saidphotonic bandgap structure comprises a second portion of said substrate;and said first portion is disposed between said active region and saidsecond portion.
 23. A structure as recited in claim 18, wherein saidphotonic bandgap structure comprises: a defect cavity; and an array ofcolumnar structures formed around said cavity.
 24. A structure asrecited in claim 23, comprising: said columnar structures having adiameter in the range of about 1.7-8.6 microns
 25. A structure asrecited in claim 24, comprising: said columnar structures having adiameter of about 2.25 microns and spacing of about 5 microns.
 26. Astructure as recited in claim 23, wherein said photonic bandgapstructure comprises: a material having a plurality of conductiveparticles disposed therein.
 27. A structure as recited in claim 26,wherein: said material comprises a high thermal conductivity material;and said particles comprise one of metal, semimetal and semiconductorparticles disposed in said material.
 28. A structure as recited in claim26, comprising: said particles having infrared transmission propertiesdifferent than infrared transmission properties of said material.
 29. Astructure as recited in claim 26, comprising: said particles beingseparated from each other by about one half to three times a wavelengthof an infrared emission peak corresponding to the respective temperatureof said structure.
 30. A structure as recited in claim 26, comprising:said particles having a size of about 1 micron and separated from eachother by a distance between about 5 and 30 microns.
 31. A structure asrecited in claim 18, wherein said photonic bandgap structure comprises:microfins enhancing both radiative and emissive heat transport.
 32. Asensing device, comprising: an infra-red sensor having a sensingsurface; and a photonic bandgap structure disposed to enhance couplingof infra-red radiation to said sensing surface.
 33. A device as recitedin claim 32, wherein said photonic bandgap structure comprises: an arrayof columnar structures formed in an array.
 34. A device as recited inclaim 33, wherein said photonic bandgap structure comprises: a defectcavity disposed in said array of columnar structures.
 35. A device asrecited in claim 32, wherein said photonic bandgap structure comprises:a material having a plurality of conductive particles disposed therein.36. A device as recited in claim 35, wherein: said material comprises ahigh thermal conductivity material; and said particles comprise one ofmetal, semimetal and semiconductor particles disposed in said material.37. A device as recited in claim 35, comprising: said particles havinginfrared transmission properties different than infrared transmissionproperties of said material.
 38. A device as recited in claim 35,comprising: said particles having a size of about 1 micron and separatedfrom each other by a distance between about 5 and 30 microns.
 39. Athermal-electric conversion device, comprising: a heat absorptionelement; a heat-to-electric conversion device coupled to said element;and a photonic bandgap structure disposed to enhance coupling of heat tosaid heat absorption device.
 40. A device as recited in claim 39,wherein said photonic bandgap structure comprises: an array of columnarstructures formed in an array.
 41. A device as recited in claim 40,wherein said photonic bandgap structure comprises: a defect cavitydisposed in said array of columnar structures.
 42. A device as recitedin claim 39, wherein said photonic bandgap structure comprises: amaterial having a plurality of conductive particles disposed therein.43. A device as recited in claim 42, wherein: said material comprises ahigh thermal conductivity material; and said particles comprise one ofmetal, semimetal and semiconductor particles disposed in said material.44. A device as recited in claim 42, comprising: said particles havinginfrared transmission properties different than infrared transmissionproperties of said material.
 45. A device as recited in claim 42,comprising: said particles having a size of about 1 micron and separatedfrom each other by a distance between about 5 and 30 microns.
 46. Adevice as recited in claim 39, comprising one of a hand-heldcomputational and communication devices receiving converted power fromsaid heat-to-electric conversion device.
 47. A device comprising: asensing device comprising: an infra-red sensor having a sensing surface,and a first photonic bandgap structure disposed to enhance coupling ofinfra-red radiation to said sensing surface, and an infra-red enhancingemission structure disposed to enhance emission of infra-red radiationto said sensor and comprising a second photonic bandgap structure.
 48. Adevice as recited in claim 47, wherein at least one of said first andsecond photonic bandgap structures comprises: an array of columnarstructures formed in an array.
 49. A device as recited in claim 48,wherein said at least one of said first and second photonic bandgapstructures comprises: a defect cavity disposed in said array of columnarstructures.
 50. A device as recited in claim 47, wherein at least one ofsaid first and second photonic bandgap structures comprises: a materialhaving a plurality of conductive particles disposed therein.
 51. Adevice as recited in claim 50, wherein: said material comprises a highthermal conductivity material; and said particles comprise one of metal,semimetal and semiconductor particles disposed in said material.
 52. Adevice as recited in claim 50, comprising: said particles havinginfrared transmission properties different than infrared transmissionproperties of said material.
 53. A device as recited in claim 50,comprising: said particles having a size of about 1 micron and separatedfrom each other by a distance between about 5 and 30 microns.
 54. Adevice, comprising: a thermal-electric conversion device comprising: aheat absorption element, a heat-to-electric conversion device coupled tosaid element, and a first photonic bandgap structure disposed to enhancecoupling of heat to said heat absorption device, a heat enhancingemission structure disposed to enhance emission of heat to said elementand comprising a second photonic bandgap structure.
 55. A device asrecited in claim 54, wherein at least one of said first and secondphotonic bandgap structures comprises: an array of columnar structuresformed in an array.
 56. A device as recited in claim 55, wherein said atleast one of said first and second photonic bandgap structurescomprises: a defect cavity disposed in said array of columnarstructures.
 57. A device as recited in claim 54, wherein at least one ofsaid first and second photonic bandgap structures comprises: a materialhaving a plurality of conductive particles disposed therein.
 58. Adevice as recited in claim 57, wherein: said material comprises a highthermal conductivity material; and said particles comprise one of metal,semimetal and semiconductor particles disposed in said material.
 59. Adevice as recited in claim 57, comprising: said particles havinginfrared transmission properties different than infrared transmissionproperties of said material.
 60. A device as recited in claim 57,comprising: said particles having a size of about 1 micron and separatedfrom each other by a distance between about 5 and 30 microns.
 61. Adevice as recited in claim 54, comprising: a waste heat source; and saidabsorption element absorbing heat from said waste heat source.
 62. Adevice as recited in claim 54, comprising: said device supplyingconverted power to a hand-held electronic device.
 63. A device asrecited in claim 62, wherein said hand-held electronic device comprisesone of a computational or communication device.